ADPD2210ACPZ-R7

Ultralow Noise, Low Power Current Amplifier ADPD2210 Data Sheet VCC FUNCTIONAL BLOCK DIAGRAM Ultralow noise, low power current amplifier 80 fA/√Hz (typical) noise floor 140 μA (typical) of supply current when active (EE = 0 μW/cm2) 100 nA (typical) of supply current in standby Flexible output configuration Optimized for pulsed systems Nominal linear output: 240 μA Space-saving 2 mm × 2 mm LFCSP package REF FEATURES BIAS VCC – (2 × VBE) POWER-DOWN LOGIC PWDN 10nA OUT IN 24 × CURRENT MIRROR 12286-101 Photoplethysmography Photodiode measurements Small current pulsed amperometry Any application requiring the ultralow noise amplification of small currents GND APPLICATIONS Figure 1. GENERAL DESCRIPTION The ADPD2210 is a low noise current amplifier designed to allow the use of smaller photodiodes by amplifying sensor signal currents by a factor of 24 while adding minimal noise. This amplification provides the system sensitivity of a large photodiode with the benefits of a smaller photodiode. A minimum linearity of 60 dB allows accurate extraction of very small time variant signals on top of large dc or low frequency offsets. The ADPD2210 is optimized for pulse mode applications such as wrist worn heart rate monitoring (HRM) or finger worn pulse oximeter oxygen saturation (SpO2), where low power consumption and rejection of ambient light is critical. In photodiode applications, the ADPD2210 holds the sensor input to within ±5 mV (typical) of the reference terminal, providing near zero-bias voltage and allowing minimal dark current and shot noise limited performance. Rev. A The ADPD2210 is designed for applications where power conservation is critical. The ADPD2210 uses very little power, typically 140 μA with no input to 954 μA at full scale. A powerdown pin places the ADPD2210 in standby when sensing is inactive. This mode adds critical time for battery-powered monitoring and can reduce battery costs in disposable applications Using the ADPD2210 to provide sensor site amplification reduces the effect of electromagnetic interference (EMI) in low level wired interfaces, providing improved signal-to-noise ratio (SNR) and rejection of interferer signals from nearby equipment. The combination of low power, high SNR, and EMI immunity enables low power system solutions not possible with traditional small current sensors, such as photodiodes plus transimpedance amplifiers (TIAs). Document Feedback Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 ©2015 Analog Devices, Inc. All rights reserved. Technical Support www.analog.com ADPD2210 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1  Pulse Mode Operation ............................................................... 11  Applications ....................................................................................... 1  Applications Information .............................................................. 12  Functional Block Diagram .............................................................. 1  Powering the ADPD2210 .......................................................... 12  General Description ......................................................................... 1  Exposed Pad Connection .......................................................... 12  Revision History ............................................................................... 2  Power-Down ............................................................................... 12  Specifications..................................................................................... 3  Reference Ouput ......................................................................... 12  Absolute Maximum Ratings............................................................ 4  Layout Considerations ............................................................... 12  Thermal Resistance ...................................................................... 4  Output Configuration ................................................................ 12  ESD Caution .................................................................................. 4  Accuracy in Clinical Applications............................................ 12  Pin Configuration and Function Descriptions ............................. 5  3-Wire Voltage Configuration .................................................. 13  Typical Performance Characteristics ............................................. 6  3-Wire Current Mode Configuration ...................................... 13  Terminology .................................................................................... 10  Evaluation Board ............................................................................ 14  Theory of Operation ...................................................................... 11  Outline Dimensions ....................................................................... 15  Overview...................................................................................... 11  Ordering Guide .......................................................................... 15  Recommended Configuration .................................................. 11  Sensitivity and SNR .................................................................... 11  REVISION HISTORY 12/15—Rev. 0 to Rev. A Changes to Ordering Guide .......................................................... 15 10/15—Revision 0: Initial Version Rev. A | Page 2 of 15 Data Sheet ADPD2210 SPECIFICATIONS VCC = 3.3 V TA = 25°C, unless otherwise noted. NSHOT is shot noise. EE is irradiance. Table 1. Parameter GAIN Current Gain DYNAMIC PERFORMANCE Power-Down Recovery Time Rise Fall Bandwidth INPUT Input Capacitance Nominal Input Current Input Offset Voltage Reference Voltage STATIC BIAS Input Referred Output Referred NOISE PERFORMANCE Current Noise Floor, Input Referred Current Noise, Input Referred Symbol Test Conditions/Comments Min Typ Max βTLA VBIAS = 0 V 23.7 24.2 24.8 tRECOVER 1% full-scale (FS) output 100 nA to 1 μA 1 μA to 10 μA 10% to 90% FS (240 μA) 90% to 10% FS (240 μA) IIN = 100 nA (dc), 100 nA (ac) IIN = 1 μA (dc), 100 nA (ac) tRISE tFALL CIN_MAX IIN_MAX VIN_REF REF IIN POWER AND SUPPLY Supply Voltage Standby Current Power Supply Rejection Ratio Supply Current Floor Supply Current VCC ISTANDBY PSRR IFLOOR ISUPPLY OUTPUT CHARACTERISTICS Maximum Output Voltage Nominal Linear Output VOUT_MAX IOUT_FS Linearity Resistor Peak Output Current Output Capacitance Output Resistance POWER-DOWN LOGIC Input Voltage High Low Leakage Current High Low IOUT_PEAK COUT ROUT IIN < 10 nA IIN = 100 nA,1.5 × NSHOT IIN = 1μA, 1.15 × NSHOT 1.8 PWDN > VIH VCC = 1.8 V to 5.0 V, EE = 10 μA IIN = 0 pA IOUT = 10 μA IOUT = 240 μA, ISUPPLY = IFLOOR + (3.3 × IOUT) VCC = 3.3 V, IOUT = 240 μA VCC = 3.3 V VCC = 1.8 V TIA, VBIAS = 0 V, RFEEDBACK = 25 kΩ IIN = 200 nA to 4 μA IIN = 200 nA to 10 μA IIN = 200 nA to 4 μA, RLOAD = 5kΩ VCC = 3.3 V VCC = 1.8 V From OUT to GND From OUT to GND VIH VIL IIH IIL 50 20 5 5 125 85 μs μs μs μs kHz kHz 8 ±5 VCC − 1.2 pF μA mV V 10 240 nA nA 10 ISB OSB 80 260 740 150 fA/√Hz fA/√Hz fA/√Hz 3.3 100 25 140 167 954 5 V nA nA/V μA μA μA VCC − 0.75 240 65 V μA μA 0.1 0.3 0.1 300 65 5 >5 VCC − 0.2 0.2 PWDN = 3.3 V PWDN = 0 V Rev. A | Page 3 of 15 Unit 0.2 −8.5 % % % μA μA pF GΩ V V nA μA ADPD2210 Data Sheet ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE Table 2. Parameter Supply Voltage, VCC Storage Temperature Range Operating Ambient Temperature Range Maximum Junction Temperature Solder Reflow Temperature (1 GΩ) of the photodiode. In applications where the REF output is used to provide an external reference or a guarding voltage, the REF output must be buffered. Failure to buffer the REF pin may adversely affect linearity above 4 μA. LAYOUT CONSIDERATIONS Working with very low currents requires special attention in layout to prevent error currents due to leakage, especially in instrumentation applications where the ADPD2210 may be located at a distance from the current source. In applications that rely on dynamic signals, parasitic capacitance must be controlled as seemingly insignificant capacitance becomes problematic with nanoampere scale signals. OUTPUT CONFIGURATION The output of the ADPD2210 allows different configurations depending on the application. The current gain of the ADPD2210 reduces the effect of surrounding interferers but, for best performance, careful design and layout is still necessary to achieve best performance. The effect of capacitance on the output must be considered carefully regardless of configuration as bandwidth and response time of the system can be limited simply by the time required to charge and discharge parasitics. Because the ADPD2210 is effectively a current source, the ADPD2210 output voltage drifts up to its compliance voltage, approximately 1.2 V below VCC, when connected to an interface that presents a high impedance. The rate of this drift is dependent on the ADPD2210 output current, parasitic capacitance, and the impedance of the load. This drift can require additional settling time in circuits following the ADPD2210 if they are actively multiplexing the output of the ADPD2210 or presenting a high impedance due to power cycling. For multiplexed systems, a current steering architecture may offer a performance advantage over a break-before-make switch matrix. ACCURACY IN CLINICAL APPLICATIONS Even with perfectly calibrated electronics, it is important to note there is no absolute in photoplethysmography measurements because they are affected by other variables, including high levels of carboxyhemoglobin or methemoglobin, density of other chromophores such as melanin, and conditions that may affect perfusion such as peripheral artery disease, shock, or hypothermia. It is important that photoplethysmography, though well suited for real-time monitoring, be supported in a clinical environment with more accurate laboratory procedures such as blood gas analysis. Rev. A | Page 12 of 15 Data Sheet ADPD2210 3-WIRE VOLTAGE CONFIGURATION 3-WIRE CURRENT MODE CONFIGURATION The ADPD2210 can be used in a minimal 3-wire voltage configuration, offering a compact solution with very few components (see Figure 25). A shunt resistor (RS) sets the transimpedance gain in front of the analog-to-digital converter (ADC). This configuration allows flexibility in matching the ADC converter full-scale input to the full-scale output of the ADPD2210. The dynamic range of the interface is limited to the compliance voltage of the ADPD2210. When used in the 3-wire current mode configuration with a photodiode (see Figure 25), the ADPD2210 is insensitive to load resistance and can be used when the signal processing is further from the sensor. EMI noise and shielding requirements are minimized; however, cable capacitance has a direct effect on bandwidth, making the 3-wire current mode configuration a better choice for unshielded interfaces. The CF value must be chosen carefully to eliminate stability and bandwidth degradation of the ADPD2210. Large capacitance around the feedback loop of the TIA has a direct effect on the bandwidth of the system. No additional amplification is needed prior to the ADC. Response time at the lower end of the range is limited by the ability of the output current to charge the parasitic capacitance presented to the output of the ADPD2210. ADPD2210 3.3V VCC 3.3V REF CURRENT IN AMPLIFIER OUT ADC AND MICROPROCESSOR RS 12286-021 GND Figure 25. ADPD2210 Used in 3-Wire Short Cable Voltage Mode Configuration with a Shunt Resistor ADPD2210 CF VCC 3.3V 3.3V RF REF OUT TIA ADC AND MICROPROCESSOR 0V TO VCC –0.75 GND 12286-022 CURRENT IN AMPLIFIER Figure 26. ADPD2210 Used in 3-Wire Current Mode Configuration with a TIA Rev. A | Page 13 of 15 ADPD2210 Data Sheet EVALUATION BOARD Figure 27 shows the evaluation board schematic. Figure 28 and Figure 29 show the evaluation board layout for the top and bottom layers, respectively. G O V P R1D DNI R2D 100kΩ C1D 0.01µF ADPD2210 1 2 PWDN VCC OUT IN C2D 1µF 6 5 D1D 1THE GND EPAD REF 4 PWDN PIN MUST BE BIASED TO VIL FOR NORMAL OPERATION AND VIH FOR STANDBY. 2R1D IS NOT NORMALLY INSTALLED BUT CAN BE POPULATED WITH A LOAD RESISTOR TO GENERATE THE VOLTAGE OUTPUT. 12286-024 3 12286-025 12286-026 Figure 27. Evaluation Board Schematic Figure 28. Evaluation Board Layout, Top Layer Figure 29. Evaluation Board Layout, Bottom Layer Rev. A | Page 14 of 15 Data Sheet ADPD2210 OUTLINE DIMENSIONS 1.70 1.60 1.50 2.10 2.00 SQ 1.90 0.65 BSC 6 PIN 1 INDEX AREA 0.15 REF 1.10 1.00 0.90 EXPOSED PAD 0.425 0.350 0.275 3 TOP VIEW 0.60 0.55 0.50 SEATING PLANE 0.05 MAX 0.02 NOM 0.35 0.30 0.25 0.20 MIN 1 BOTTOM VIEW PIN 1 INDICATOR (R 0.15) FOR PROPER CONNECTION OF THE EXPOSED PAD, REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SECTION OF THIS DATA SHEET. 0.20 REF 02-06-2013-D 4 Figure 30. 6-Lead Lead Frame Chip Scale Package [LFCSP_UD] 2 mm × 2 mm Body, Ultra Thin, Dual Lead (CP-6-3) Dimensions shown in millimeters ORDERING GUIDE Model1 ADPD2210ACPZ-R7 ADPD2210ACPZ-RL EVALZ-ADPD2210 1 Temperature Range −40°C to +85°C −40°C to +85°C Package Descriptions 6-Lead Lead Frame Chip Scale Package [LFCSP_UD] 6-Lead Lead Frame Chip Scale Package [LFCSP_UD] Evaluation Board Z = RoHS Compliant Part. ©2015 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D12286-0-12/15(A) Rev. A | Page 15 of 15 Package Option CP-6-3 CP-6-3